1. Field of the Invention
This invention relates to a rear light condition detecting device for a camera and more particularly to a device which determines a rear-light shot condition from a combination of information on the distance to an object to be photographed and information on the luminance of the object.
2. Description of the Prior Art
In order to adequately perform an exposure for a picture taking plane as a whole, cameras in general employ an averaging light measuring method in which an average value of luminance information for the whole picture plane is obtained. However, where the sunlight is directly incident on the picture plane, the average light measurement value increases, resulting in a photograph in which the main object is extremely underexposed.
To avoid such a result, it is necessary to detect a rear light condition and to make spot light measurement giving priority to information on the luminance of the main object. In a method heretofore employed for automatically carrying out this operation, the luminance of the middle of the picture taking plane is compared with the average luminance of the whole picture plane. If the difference between them is above a predetermined value, the photography object is considered to be in a rear light condition and a spot light measurement is carried out giving priority to the luminance of the middle of the picture plane. In other words, although the location of the main object is known only by the photographer, the main object to be photographed is in the middle of the picture plane in the majority of cases. Therefore, in this method, the luminance of the middle of the picture taking plane is simply assumed to represent the luminance of the main object and a rear light condition correcting operation is automatically carried out without recourse to manual adjustment by the photographer. Thus, in cases where the luminance of the middle part is much lower than the average luminance of the whole picture plane, the object is determined to be under a rear light condition brought about by the sunlight or the like.
In accordance with this method, however, if the main object is not located in the middle part of the picture taking plane, the object is either determined not to be under a rear light condition when it is actually under a rear light condition or no spot light measurement is carried out even when it is determined to be under a rear light condition. Therefore, in such a case, rear light correction cannot be adequately carried out.
Furthermore, in a generally practiced method for coping with a rear light condition, the main object is imparted with an apposite luminance by illuminating it with a flash light of a flash device. However, the light of the flash device would not reach the main object if it is located far away. In that event, the flash light not only fails to correct the rear light condition but would rather increase the difference between the luminance of the main object and the average luminance of the whole picture taking plane.
A first object of this invention is to provide a rear light detecting device for a camera, wherein distances to a plurality of parts appearing within a picture taking plane are measured on the assumption that an object located nearby is the main object to be photographed or that a light source, such as the sun, is among faraway objects; and the luminance of the main object is compared with that of other objects to determine that the main object is under a rear light condition if the luminance of the main object is much lower than the luminance of others or if the luminance of the faraway objects is much greater than others, so that a rear light condition can be accurately determined regardless of the position of the main object within the picture taking plane.
A second object of this invention is to provide a rear light detecting device for a camera, wherein, when the external world is judged to be bright and in a rear light condition, if an object to be photographed is located at a near distance, the object is illuminated by the light of a flash device; and, if the object to be photographed is located at a medium or far distance, an automatic exposure (AE) time of the camera is shifted to a longer exposure time value.
These and further objects and features of this invention will become apparent from the following detailed description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.